Total Alkalinity and Buffering Power

[vindee]

My water report shows a total alkalinity of 36 ppm. How does this relate to buffering power?

Calcium 9.9 ppm
Magnesium 2 ppm
Bicarbonate 44 pmm
Sulfate 1 ppm
Total Hardness 33 pmm
Sodium 5 ppm

 

[day_trippr]

Not a lot. Imo, that is A Good Thing
Should be very good for brewing water as you can push it anywhere you want...

Cheers!

 

[VikeMan]

The higher your total alkalinity, the higher the buffering capacity. A total alkalinity of 36 ppm is fairly low. This means that it's relatively easy to move the pH of the water via acid additions.

 

[vindee]

Great! Thank you.
This is natural spring water I go up and get every few weeks for drinking and brewing. I am finally trying to make educated water adjustments instead if just guessing on them.

 

[Silver_Is_Money]

36 mg/L/50.04345 = 0.7194 mEq/L of Alkalinity (As CaCO3)
(Where: mEq = MilliEquivalent)

If your desire is to reduce sparge water Alkalinity to zero, you must reduce its pH to 4.3. But the general goal is to reduce it to ~5.4 pH, and this requires only around 90% of the acidity that would be required for a reduction to pH 4.3. So effectively the mg/L Alkalinity to be reduced whereby to hit pH ~5.4 is:

36 x ~0.90 = ~32.4 mg/L

32.4 mg/L/50.04345 = 0.6474 mEq/L of Alkalinity to be removed whereby to hit ~pH 5.4

88% Lactic Acid has an acid strength of 11.451 mEq/mL at pH 5.4

0.6474/11.451 ~= 0.0565 mL of 88% Lactic Acid required to move 1L of 36 mg/L Alkalinity water to pH 5.4

So you could make the argument that the Buffering Capacity of 1L your water at pH 5.4 is ~ equivalent to 0.0565 mL of 88% Lactic Acid

To reduce 19L (~5 Gal.) of your water to pH 5.4 should require 19 x ~0.0565 = ~1.07 mL of 88% Lactic Acid added to it.

 

[vindee]

Good stuff. Thanks for the info!

 

[Silver_Is_Money]

The pH of your water isn't specified, but if we presume 7.1 pH and we further presume that for water in general 1L has a nominal weight of 1 Kg. we can compute your waters linear slope BC as follows:

Delta-pH = mEq/(BC x Kg.)
(7.1-5.4) = 0.6474/(BC x 1L)
1.7 x BC = 0.6474
BC_Water = 0.3808 mEq/L.pH

This means that for every 1.0 pH units that we want to move 1 Liter of your water we must add to it 0.3808 mEq of acid. This linear slope approach to buffering capacity should serve ballpark reasonably only over "modest" Delta-pH shifts away from the originally targeted pH of 5.4, since pH is exponential and not linear.

For example, if you desired to only reduce the pH of one liter of your water to 6.0 as opposed to 5.4:

(7.1-6.0) = mEq_Acid/(0.3808 x 1L)
1.1 = mEq_Acid/0.3808
mEq_Acid = 0.4189 (required to be added whereby to move 1L to pH 6.0)

88% Lactic Acid has an acid strength of 11.697 mEq/mL relative to our pH target of 6.0, so therefore:

0.4189 mEq / 11.697 mEq/mL = 0.03581 mL of 88% Lactic Acid required to be added per Liter of your water

For 5 gallons, which equals 18.927 Liters:

18.927 x 0.03851 ~= 0.68 mL of 88% Lactic Acid to be added whereby to move 5 gallons of 36 mg/L Alkalinity and pH 7.1 water to a targeted pH of 6.0.